I have found a pedal that will allow me to retain some lowend when using a fuzz and guitar overdrive pedal. The pedal is the LPB-1 power booster nano by electro harmonix. i use a Boss Od-3 guitar overdrive (not to be confused with the bass one ODB-3) and an electro Harmonix Little big Muff. When I turn on the muff i normally lose a large chunk of low end but with the booster on it keeps some low end. I am not saying that this is a cure for the problem but it seems to help me a good bit.